1. Field of the Invention
The present invention relates to a digital video cassette recorder where digital signals are subjected to high efficiency compression for recording and in particular to slow reproduction of signals in such a digital video cassette recorder.
2. Description of Prior Art
In a digital video cassette recorder, video signals are digitized, and the digital signals are subjected to high efficiency coding and recorded in a plurality of tracks with helical scan. Slow reproduction is a function of a digital video cassette recorder, and signal processing on slow reproduction is described, for example, in Japanese Patent laid open Publications 3-132183/1991, 5-344472/1993 and 9-261591/1997.
In a prior art digital video cassette recorder described in Japanese Patent laid open Publication 3-132183/1991, signals consist of a series of unit period such as horizontal period (referred to as block), and an index signal is added to each block. An index number indicates a number of field to which the block belongs and a number of block. When signals are reproduced, an index number is reproduced to determine which field is to be reproduced. Reproduced signals are subjected to error correction and the like for each block and stored in a frame memory. In slow reproduction, the data of one field stored in the frame memory are read in the unit of field according to change in the detected index number.
In the digital video cassette recorder, the index numbers added on recording are reproduced, and the output field is controlled on reproduction. However, if data are subjected to high efficiency compression in the unit of field or frame and subjected to shuffling recording, index number cannot be defined when signals are recorded. Then, the output field cannot be controlled.
Another prior art digital video cassette recorder described in Japanese Patent laid open Publication 5-344472/1993 solves this problem. Data are compressed at a high efficiency in the unit of fields (group) and subjected to shuffling recording. When compressed data in a plurality of fields (or a group) are read, truck index numbers which have been added on recording are reproduced to detect which position is reproduced. Signals of each field are output according to the detection in the unit of group. However, when compressed data are reproduced, the output of data are completed in each group. Then, the output time for a field on slow reproduction varies largely among fields. Thus, the reproduced pictures are not smooth on slow reproduction.
In a prior art digital image signal reproduction apparatus described in Japanese Patent laid open Publication 9-261591/1997, when compressed image data are read in the unit of a plurality of fields (or a group), the last field in a group and the first field in a following field can be output as one frame in slow reproduction. Then, the output of the reproduced images is improved to continue more smoothly. However, though the operation at a particular reproduction speed is described, it is not described how the slow reproduction is controlled at any reproduction speed.
An object of the present invention is to provide an apparatus where an image can be reproduced smoothly on slow reproduction.
An apparatus according to the invention reproduces data recorded on a tape in slow reproduction. The digital video signals are compressed and recorded in predetermined M tracks (Mxe2x89xa71) on a tape with helical scan in the unit of a page consisting of N frames (Nxe2x89xa71), and position data representing position in the M tracks are added to the digital data on recording at predetermined positions in the M tracks. A reproduction processor converts signals reproduced from a magnetic tape to compressed digital data. A decoder decodes the compressed digital data reproduced by the reproduction processor to digital data, and a first storage device stores the decoded data in the unit of N frames. Further, a second storage device delays data received from the first storage device by a time of a frame. On the other hand, a position detector detects the position data in the data reproduced by the reproduction processor to determine which reproduction position is reproduced in an area where the data in a page are recorded. Thus, the situation of data reproduction is observed by detecting the position data. A read controller receives the reproduced position during a frame period and generates a control signal according to the determined reproduction position observed during a frame period. The control signal is determined to make output time of a frame even. A memory controller controls read from the first storage device according to the control signal, while a switch selects data to be output between data received from the first storage device and data received from the second storage device according to the control signal.
Preferably, a frame consists of two fields. The second storage device delays data received from the first storage device by a time of a field. The read controller generates the control signals by checking whether reproduction of an area of M/(2N) tracks of an area recording the data of one page is completed in the former half or in the latter half of a frame period and whether the completion of the reproduction of an area of M/(2N) tracks is zero, one or two times in a frame period, the control signal being determined to make output time of a field even.
Preferably, the memory controller controls the reading according to a combination of the control signal of a prior frame and that of a current frame.
Preferably, the switch selects the data to be output according to a combination of the control signal of a prior frame and that of a current frame.
Preferably, the decoder comprises an inner correction decoder and an outer correction decoder. The position data are added to the digital data subjected to outer correction. The inner correction decoder subjects the data reproduced by the reproduction processor to inner correction decoding. The read controller receives the data from the first inner correction decoder and detects the position data therein.
Preferably, the position data includes a first position information representing a position in a track and a second position information representing a track in the M tracks.
Preferably, the position detector determines the second position information detected at the last in a scan and detects the first position information detected first after the determined second position information is changed.
Preferably, the second position information is recorded to have a margin relative to a data to be determined currently.
Preferably, data are recorded to the tape with shuffling in the M tracks and the reproduction processor converts the recorded data to the digital data without shuffling.
Preferably, the read controller generates the control signal further by taking direction of tape running into account.
In a method according to the invention for reproducing signals recorded on a tape in slow reproduction, the signals are compressed to digital data and recorded in M tracks (Mxe2x89xa71) on a tape with helical scan in the unit of a page consisting of N frames (Nxe2x89xa71), and position data representing position in the M tracks are added to the digital data on recording at predetermined positions in the M tracks. On reproduction, signals reproduced from a magnetic tape are converted to compressed digital data. The reproduced digital data are decoded and the decoded data are stored in a first storage device in the unit of N frames. Further, data received from the first storage device are stored in a second storage device for delay by a time of a frame. On the other hand, the position data in the reproduced data are detected to determine which reproduction position is reproduced in an area where the data in a page are recorded. A control signal is generated according to the determined reproduction position observed during a frame period, the control signal being determined to make output time of a frame even. Reading from the first storage device is controlled according to the control signal, and data to be output are selected according to the control signal between data received from the first storage device and data received from the second storage device.
Preferably, in the method, a frame consists of two fields. The data received from the first storage device are delayed by a time of a field. The control signals is generated by checking whether reproduction of an area of M/(2N) tracks of an area recording the data of one page is completed in the former half or in the latter half of a frame period and whether the completion of the reproduction of an area of M/(2N) tracks is zero, one or two times in a frame period. The control signal is determined to make output time of a field even.
Preferably, in the method, the position data includes a first position information representing a recording position in a track and second position information representing a track position in the M tracks.
An advantage of the present invention is that images can be reproduced smoothly on slow reproduction in a digital video cassette recorder.